enhanced-resolve

What is enhanced-resolve?

The enhanced-resolve package is a highly configurable module resolution library for Node.js, which is used by webpack under the hood. It resolves a path to a file or directory in a file system. It can handle complex resolution patterns like module aliases, extensions, and directories with package.json files.

What are enhanced-resolve's main functionalities?

File Resolution

Resolves the path to a file, taking into account file extensions and processing according to the configuration provided.

const { ResolverFactory } = require('enhanced-resolve');

const resolver = ResolverFactory.createResolver({
  fileSystem: require('fs'),
  extensions: ['.js', '.json']
});

resolver.resolve({}, __dirname, './path/to/file', (err, result) => {
  if (err) console.error(err);
  else console.log(result);
});

Directory Resolution

Resolves the path to a directory, looking for the 'main' field in the package.json or index.js within that directory.

const { ResolverFactory } = require('enhanced-resolve');

const resolver = ResolverFactory.createResolver({
  fileSystem: require('fs'),
  mainFields: ['main']
});

resolver.resolve({}, __dirname, './path/to/directory', (err, result) => {
  if (err) console.error(err);
  else console.log(result);
});

Plugin System

Allows the use of plugins to extend or modify the resolution behavior, providing a high degree of customization.

const { ResolverFactory } = require('enhanced-resolve');
const MyPlugin = require('./MyPlugin');

const resolver = ResolverFactory.createResolver({
  fileSystem: require('fs'),
  plugins: [new MyPlugin()] // Custom plugin to modify resolution behavior
});

// Use the resolver as before

Other packages similar to enhanced-resolve

resolve

A simple module resolution package that can be used to resolve file paths similarly to Node's 'require.resolve'. It is less configurable than enhanced-resolve but is easier to use for simple resolution tasks.

browser-resolve

A browser-focused module resolver that aims to replicate Node's 'require.resolve' behavior for browser environments. It is similar to enhanced-resolve but with a focus on resolving modules for bundling in the browser.

require-resolve

This package provides a function to resolve a module path relative to a given path. It is a simpler alternative to enhanced-resolve, focusing on resolving require paths without the extensive configuration options.

README

enhanced-resolve

Offers an async require.resolve function. It's highly configurable.

Features

• plugin system
• provide a custom filesystem
• sync and async node.js filesystems included

Getting Started

Install

# npm
npm install enhanced-resolve
# or Yarn
yarn add enhanced-resolve

Creating a Resolver

The easiest way to create a resolver is to use the createResolver function on ResolveFactory, along with one of the supplied File System implementations.

const {
  NodeJsInputFileSystem,
  CachedInputFileSystem,
  ResolverFactory
} = require('enhanced-resolve');

// create a resolver
const myResolver = ResolverFactory.createResolver({
  // Typical usage will consume the `NodeJsInputFileSystem` + `CachedInputFileSystem`, which wraps the Node.js `fs` wrapper to add resilience + caching.
  fileSystem: new CachedInputFileSystem(new NodeJsInputFileSystem(), 4000),
  extensions: ['.js', '.json']
  /* any other resolver options here. Options/defaults can be seen below */
});

// resolve a file with the new resolver
const context = {};
const resolveContext = {};
const lookupStartPath = '/Users/webpack/some/root/dir';
const request = './path/to-look-up.js';
myResolver.resolve({}, lookupStartPath, request, resolveContext, (err/*Error*/, filepath/*string*/) => {
  // Do something with the path
});

For more examples creating different types resolvers (sync/async, context, etc) see lib/node.js.

Resolver Options

Field	Default	Description
alias	[]	A list of module alias configurations or an object which maps key to value
aliasFields	[]	A list of alias fields in description files
cacheWithContext	true	If unsafe cache is enabled, includes request.context in the cache key
descriptionFiles	["package.json"]	A list of description files to read from
enforceExtension	false	Enforce that a extension from extensions must be used
enforceModuleExtension	false	Enforce that a extension from moduleExtensions must be used
extensions	[".js", ".json", ".node"]	A list of extensions which should be tried for files
mainFields	["main"]	A list of main fields in description files
mainFiles	["index"]	A list of main files in directories
modules	["node_modules"]	A list of directories to resolve modules from, can be absolute path or folder name
roots	[]	A list of directories to resolve request starting with / from
ignoreRootsErrors	false	Ignore fatal errors happening during handling of roots (allows to add roots without a breaking change)
preferAbsolute	false	Prefer to resolve server-relative urls as absolute paths before falling back to resolve in roots
unsafeCache	false	Use this cache object to unsafely cache the successful requests
plugins	[]	A list of additional resolve plugins which should be applied
symlinks	true	Whether to resolve symlinks to their symlinked location
cachePredicate	function() { return true };	A function which decides whether a request should be cached or not. An object is passed to the function with path and request properties.
moduleExtensions	[]	A list of module extensions which should be tried for modules
resolveToContext	false	Resolve to a context instead of a file
restrictions	[]	A list of resolve restrictions
fileSystem		The file system which should be used
resolver	undefined	A prepared Resolver to which the plugins are attached

Plugins

Similar to webpack, the core of enhanced-resolve functionality is implemented as individual plugins that are executed using Tapable. These plugins can extend the functionality of the library, adding other ways for files/contexts to be resolved.

A plugin should be a class (or its ES5 equivalent) with an apply method. The apply method will receive a resolver instance, that can be used to hook in to the event system.

Plugin Boilerplate

class MyResolverPlugin {
  constructor(source, target) {
    this.source = source;
    this.target = target;
  }

  apply(resolver) {
    const target = resolver.ensureHook(this.target);
    resolver.getHook(this.source).tapAsync("MyResolverPlugin", (request, resolveContext, callback) => {
      // Any logic you need to create a new `request` can go here
      resolver.doResolve(target, request, null, resolveContext, callback);
    });
  }
}

Plugins are executed in a pipeline, and register which event they should be executed before/after. In the example above, source is the name of the event that starts the pipeline, and target is what event this plugin should fire, which is what continues the execution of the pipeline. For an example of how these different plugin events create a chain, see lib/ResolverFactory.js, in the //// pipeline //// section.

Tests

npm test

Passing options from webpack

If you are using webpack, and you want to pass custom options to enhanced-resolve, the options are passed from the resolve key of your webpack configuration e.g.:

resolve: {
  extensions: ['', '.js', '.jsx'],
  modules: ['src', 'node_modules'],
  plugins: [new DirectoryNamedWebpackPlugin()]
  ...
},

License

Copyright (c) 2012-2016 Tobias Koppers

MIT (http://www.opensource.org/licenses/mit-license.php)